Author

Date of Issue

2010

School

School of Civil and Environmental Engineering

Research Centre

Nanyang Environment and Water Research InstituteSingapore Membrane Technology Centre

Abstract

Poly(ethylene chlorotrifluoroethylene) (ECTFE) is a 1:1 alternating copolymer of ethylene and chlorotrifluoroethylene
that offers excellent resistance in chemically and thermally challenging environments.
ECTFE membranes with a variety of microstructures have been fabricated via thermally induced phase
separation (TIPS) with dibutyl phthalate (DBP) as the diluent. A continuous flat sheet extrusion apparatus
with a double rotating drum was used that permitted controlling both the casting solution thickness and
axial tension on the nascent membrane. Initial compositions of ECTFE/DBP solutions in the liquid–liquid
region of the binary phase diagram were chosen, resulting in membranes with an interconnected pore
structure. The effects of several important process parameters were studied to determine their effect
on the structure and properties of the membrane. The parameters evaluated included the initial ECTFE
concentration, cooling rate, membrane thickness, co-extrusion of diluent, and stretching of the nascent
membrane. The resulting membranes were characterized using SEM, porometry, and permeation measurements.
For the range of process parameters studied, ECTFE membranes exhibited a decrease in surface
porosity with increasing initial polymer concentration and cooling rate. The effect of membrane thickness
on the permeation flux was not significant. Co-extrusion of diluent increased the surface porosity
and eliminated the dense skin that was otherwise present under rapid cooling conditions. Subsequent
stretching of the nascent membrane resulted in a more open structure and a significant increase in the
permeation flux.